Anesthesiology
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Comparative Study
Effects of general anesthetics on intercellular communications mediated by gap junctions between astrocytes in primary culture.
Astrocytes represent a major nonneuronal cell population in the central nervous system (CNS) and are actively involved in several brain functions. These cells are coupled by gap junctions (GJ) into a syncytial-like network resulting in cellular communication through ionic and metabolic exchange between adjacent astrocytes. Whether anesthetics affect astrocyte function is not known. In the present study, the effects of general anesthetics on GJ permeability were investigated in primary cultures of mouse striatal astrocytes. ⋯ These results indicate that general anesthetics differentially affect GJ permeability in cultured astrocytes. This uncoupling effect (closure of gap junctions) may contribute to the mechanisms of action of some anesthetic agents (primarily volatile anesthetics) at the level of the CNS by altering astrocyte communication.
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Neuromuscular blockade (NMB) is a frequent component of anesthetic techniques used during surgery in which monitoring of the nervous system is desirable. Because NMB should affect the evoked muscle response to transcranial magnetic stimulation (tcMMEP), their relationship in a primate model was characterized. ⋯ This study indicates that tcMMEP onset latency is not significantly affected by NMB if the degree of blockade in the muscles used for tcMMEP monitoring is not extreme (greater than 0.2 of baseline by m-response amplitude or a TOF ratio of 0.1 or greater). If monitoring of tcMMEP amplitude is desired, partial neuromuscular blockade may be acceptable. However, amplitude reduction may occur during partial NMB. Maintenance of a constant degree of NMB is suggested to minimize amplitude fluctuations.
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Clinical Trial
Effect of a vecuronium-induced partial neuromuscular block on hypoxic ventilatory response.
A previous study has demonstrated a decrease in the hypoxic ventilatory response in volunteers partially paralyzed with vecuronium. However, in this study, hypocapnia was allowed to occur. Because hypocapnia counteracts the ventilatory response to hypoxia during partial vecuronium-induced neuromuscular block and isocapnia, the hypoxic ventilatory response (HVR) was tested in 10 awake volunteers. ⋯ We conclude that a vecuronium-induced partial neuromuscular block impairs HVR more than it does HCVR in humans, suggesting an effect of vecuronium on carotid body hypoxic chemosensitivity.
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The subcutaneous injection of formalin in the rat paw results in several minutes of flinching (phase 1) followed by cessation of activity then resumption of flinching (phase 2), which depends on facilitation of spinal transmission evoked by C-fiber activity generated immediately after the noxious stimulus. It was hypothesized that suppression of dorsal horn activity during and immediately after formalin injection by inhalation anesthetics or intrathecal opiates would block spinal facilitation and inhibit phase 2 flinching, even if the anesthetic or opiate were eliminated before phase 2. ⋯ Isoflurane, even at high concentrations, administered during and shortly after a noxious stimulus produces only a modest reduction in facilitation of afferent processing. The addition of intrathecal morphine during the period of nociceptor activity results in marked attenuation of the facilitated state.